The best method to calculate the scale factor between a pre-image and its image is to "Find the lengths of corresponding sides and then set up a ratio of image to pre-image and then divide." Option B
Calculating the scale factor of a pre-image and image involves identifying corresponding sides in the pre-image and its image and then setting up a ratio of the lengths of these corresponding sides in the image over the lengths of the corresponding sides in the pre-image.
Dividing these lengths produces the scale factor, which represents the proportion by which the pre-image has been enlarged or reduced to create the image.